On 8/27/25 4:26 PM, Brett A C Sheffield wrote:

On 2025-08-27 08:23, Oscar Maes wrote:

quoted

Add test to check the broadcast ethernet destination field is set
correctly.

This test sends a broadcast ping, captures it using tcpdump and
ensures that all bits of the 6 octet ethernet destination address
are correctly set by examining the output capture file.

Signed-off-by: Oscar Maes <redacted>
---
Link to discussion:
https://lore.kernel.org/netdev/20250822165231.4353-4-bacs@librecast.net/ (local)

Thanks to Brett Sheffield for writing the initial version of this
selftest!

Thanks for leaving my author name in the file.  Perhaps you might consider
adding:

Co-Authored-By: Brett A C Sheffield [off-list ref]

to your commit message. I spend quite a bit of my Saturday bisecting and
diagnosing,  and writing the patch and test.

I don't want to delay the fix, since I received other reports for the
same problem, but I think proper recognition should be agreed by all the
involved parties.

I'm going to apply patch 1/2 standalone, to allow repost for this one.

quoted

 tools/testing/selftests/net/Makefile          |  1 +
 .../selftests/net/broadcast_ether_dst.sh      | 82 +++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100755 tools/testing/selftests/net/broadcast_ether_dst.sh

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index b31a71f2b372..56ad10ea6628 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile

@@ -115,6 +115,7 @@ TEST_PROGS += skf_net_off.sh
 TEST_GEN_FILES += skf_net_off
 TEST_GEN_FILES += tfo
 TEST_PROGS += tfo_passive.sh
+TEST_PROGS += broadcast_ether_dst.sh
 TEST_PROGS += broadcast_pmtu.sh
 TEST_PROGS += ipv6_force_forwarding.sh
 

diff --git a/tools/testing/selftests/net/broadcast_ether_dst.sh b/tools/testing/selftests/net/broadcast_ether_dst.sh
new file mode 100755
index 000000000000..865b5c7c8c8a
--- /dev/null
+++ b/tools/testing/selftests/net/broadcast_ether_dst.sh

@@ -0,0 +1,82 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Author: Brett A C Sheffield <bacs@librecast.net>
+# Author: Oscar Maes <oscmaes92@gmail.com>
+#
+# Ensure destination ethernet field is correctly set for
+# broadcast packets
+
+source lib.sh
+
+CLIENT_IP4="192.168.0.1"
+GW_IP4="192.168.0.2"
+
+setup() {
+	setup_ns CLIENT_NS SERVER_NS
+
+	ip -net "${SERVER_NS}" link add link1 type veth \
+		peer name link0 netns "${CLIENT_NS}"
+
+	ip -net "${CLIENT_NS}" link set link0 up
+	ip -net "${CLIENT_NS}" addr add "${CLIENT_IP4}"/24 dev link0
+
+	ip -net "${SERVER_NS}" link set link1 up
+
+	ip -net "${CLIENT_NS}" route add default via "${GW_IP4}"
+	ip netns exec "${CLIENT_NS}" arp -s "${GW_IP4}" 00:11:22:33:44:55
+}
+
+cleanup() {
+	rm -f "${CAPFILE}"
+	ip -net "${SERVER_NS}" link del link1
+	cleanup_ns "${CLIENT_NS}" "${SERVER_NS}"
+}
+
+test_broadcast_ether_dst() {
+	local rc=0
+	CAPFILE=$(mktemp -u cap.XXXXXXXXXX)
+
+	echo "Testing ethernet broadcast destination"
+
+	# start tcpdump listening for icmp
+	# tcpdump will exit after receiving a single packet
+	# timeout will kill tcpdump if it is still running after 2s
+	timeout 2s ip netns exec "${CLIENT_NS}" \
+		tcpdump -i link0 -c 1 -w "${CAPFILE}" icmp &> /dev/null &
+	pid=$!
+	sleep 0.1 # let tcpdump wake up

Here you could use slowwait checking for packet socket creation, to be
more robust WRT very slow env.

/P